| disj(x, y), a ∈ y, disj(a ' + x, y) ⊦ |
∀ x, a. ¬(disj(x, y0) ∧ a ∈ y0 ∧ disj(a ' + x, y0)), disj(x, a0 + y0), a ∈ a0 + y0, disj(a ' + x, a0 + y0) ⊦
Used simplifier rules: e: ⊦ disj(x, []);%list freely generated by [], +;;%in-empty: ⊦ ¬ a ∈ []; from specification list